Rainfall

2010 was one of the driest years on record across the Perth Metropolitan area.
Lowest annual rainfall records were broken at a number of sites due to a culmination
of a record dry summer, a record dry winter and below average rainfall in spring.
Annual rainfall totals were generally 40 to 50 % lower than normal and in the
350-600 mm range. Mundaring in the Perth hills registered 599.6 mm in 2010 which
was the driest year in 107 years of record, and the first annual rainfall total
of below 600 mm. The previous lowest annual rainfall record at Mundaring was
653.4 mm in 1914.

Perth Metro recorded 503.8 mm on 65 rain days in 2010, which was the second
driest year on record since records commenced in 1876, behind the 466.8 mm in
2006. The 65 rain days was the lowest number of rain days recorded in a year
at Perth Metro, the previous record being 88 rain days in 1969. March (total
40.4 mm; average 19.4 mm) and December (total 17.4 mm; average 12.8 mm) were
the only two months in 2010 where Perth Metro received rainfall above the monthly
average. The wettest day for Perth Metro in 2010 was 9 July when 40.6 mm was
recorded, which was the wettest July day since 88.8 mm was recorded on the 30
July 2001.

Extended dry spells, which began in late spring (21 November 2009), were observed
at many stations in the Perth area over summer 2009-10, and into March 2010.
Perth Airport registered 122 continuous days without measurable rain from 21
November 2009 to 22 March 2010, breaking the previous longest dry spell of 83
days between 24 December 1947 and 15 March 1948. Perth Metro observed 78 days
without measurable rainfall from 21 November 2009 to 7 February 2010, when 0.2
mm was recorded, which was Perth Metro's second longest dry spell on record.
The longest dry spell at Perth Metro was 83 days between 15 December 1974 and
7 March 1975.

Severe storms swept through the Perth metropolitan area on the afternoon of
22 March, bringing the first significant rainfall to Perth since 19 November
2009. The storm was considered to be one of the worst in Perth's history with
damage estimated at over $1 billion, caused mainly by large hail (up to 6 cm)
and flash flooding. The highest daily rainfall total recorded in Perth during
the event (and for autumn) was 66.8 mm at Wanneroo (DAFWA), whilst Jarrahdale
recorded 57.2 mm. For more details of the severe thunderstorms in Perth, please
read the storm
summary.

Maximum temperature

2010 was one of the hottest years on record for most of the Perth Metropolitan
area, apart from Rottnest Island. A number of sites observed their hottest year
on record with annual mean maximum temperatures 1 °C to 1.5 °C above
normal and mostly in the 24 to 26 °C range.

Perth Metro's annual mean daily maximum temperature in 2010 was 25.3 °C,
which was the warmest year on record since records commenced in 1897. The previous
record was 25.2 °C in 1978, whilst the third highest was 25.0 °C in
2009, so Perth Metro has recorded two of its three hottest years in the past
two years. Daily maxima in 2010 at Perth Metro ranged from a very hot 42.9 °C
on 17 January to a cool 13.3 °C on 9 July. During 2010, Perth Metro recorded
65 hot days (a hot day is when the daily maximum temperature is 32 °C or
higher), which is the second greatest number of hot days behind the 66 days
in 1978.

Heatwave conditions (three or more days of maximum temperature over 35°C)
were observed at several Perth sites during summer 2009-10 and into the first
two days of autumn: 2 to 5 January; 17 to 19 January; and 24 February to 2 March.
During the second hot spell (17-19 January), Perth Airport recorded three days
with daily maximum temperatures above 42 °C, which had only occurred once
before at the airport (18 and 21 January 1961) since records began in 1944.
Perth Metro recorded three days with daily maximum temperatures above 41.0 °C
from 17 to 19 January. A run of three days over 41°C had happened on only
two other occasions at the official Perth site since recording began in 1897
(13 to 15 March 1922 and 7 to 9 February 1933). The hottest temperature for
2010 at most sites was registered during this time, with Pearce RAAF recording
the hottest daily maximum for the year in the Perth metropolitan area with 44.2
°C on 18 January 2010.

Spring in 2010 was notable for being the hottest on record for most sites in
the Perth area, including Perth Metro and Rottnest Island, which both registered
their warmest spring since records commenced in 1897. Medina Research Centre
registered a daily maximum temperature of 41.4 °C on 19 November which was
their highest spring temperature in 26 years of record.

Minimum temperature

Annual mean minimum temperatures in 2010 were near average in the Perth region,
mostly in the 11 °C to 15 °C range. The annual mean minimum temperature
at Pearce RAAF in 2010 was 0.6 °C cooler than normal, the biggest departure
in the Perth area, whilst Perth Metro's annual mean daily minimum temperature
in 2010 was 12.4 °C, which was 0.3 °C below normal.

Perth Metro recorded 12 warm nights during January 2010 (a warm night in Perth
is when the overnight minimum temperature is 20°C or higher), which is equal
to the record set in January 1995. The average for January is six. The the warmest
night for the year at Perth Metro was 28.1 °C on 12 March, Perth Metro's
second warmest March night on record, and eighth warmest night for any month.

Averaged over the three winter months of 2010, minimum temperatures were very
much below average for most sites in the Perth area. Perth Metro, Pearce RAAF
and Gosnells City registered their lowest mean minimum temperature for winter
on record with a significant run of cold nights (nights with minima less than
5 °C) occurring during June and July across the Perth metropolitan area.
Perth Airport recorded 15 consecutive cold nights from 24 June to 8 July, its
longest run of cold nights in 66 years of record, and easily passing the previous
record of 11 consecutive cold nights in winter 1990. Perth Metro recorded 37
cold nights (nights with minima less than 5 °C) during winter 2010, whch
equalled the record for the Perth Metro (Mt Lawley) site set in 2001, and also
included a record run of 15 consecutive cold nights from the 24 June to the
8 July. During this event, Perth Metro observed a very cold -0.6 °C on 26
June, which was its second coldest night on record behind the -0.7 °C on
17 June 2006; while Jandakot registered the coldest night in the metropolitan
area in 2010 with -2.5 °C.

Wind & sunshine

Ocean Reef observed the highest wind gust for the Perth area in 2010 with 120
km/h at 1548 WST on 22 March during the March hailstorm.

Annual mean daily sunshine hours recorded at Perth Airport was 9.2 hours, which
was the sunniest year since records commenced in Perth in 1898. The previous
record was 9.1 hours in 1994.

Notes

A Annual Climate Summary is prepared to list the main features of the weather in Perth using the most timely and accurate information available on the date of publication; it will generally not be updated. Later information, including data that has had greater opportunity for quality control, will be presented in the Monthly Weather Review, usually published in the fourth week of the month.

This statement has been prepared based on information available at
5 pm on Tuesday 4 January 2011.
Some checks have been made on the data, but it is possible that results will change
as new information becomes available.

Averages are long-term means based on observations from all available
years of record, which vary widely from site to site. They are not shown for
sites with less than 10 years of record.
The median
is sometimes more representative than the
mean
of long-term average rain.

The Rank indicates how rainfall this time compares with the climate record for the site,
based on the
decile ranking
(very low rainfall is in decile 1, low in decile 2 or 3,
average in decile 4 to 7, high in decile 8 or 9
and very high is in decile 10).
The Fraction of average shows how much rain has fallen this time as a
percentage of the long-term mean.

Records in this summary are based on sites with at least 10 years of data.

*Official Perth observations have been recorded at several different sites
with varying instrumentation over the years, and these changes can affect
the continuity of the climate record. For the current Mt Lawley site, the
most significant changes of this kind relate to minimum temperature and
rain days.

For that reason, current mean temperature and rain-day data quoted here are
based only on readings from the Mt Lawley site, which commenced observations in 1993.
Sunshine recordings are from Perth Airport and for similar reasons current means use
only Perth Airport data, which commenced in 1993.

For PDF files of Perth Metro climate statistics for other months, please click
here
for extremes and
here
for averages.